Today, prostheses of this kind are well known from the prior art. A liner is often first pulled over the amputation stump. This liner can be made of a silicone material or a polyurethane material, for example, which has been adapted to the individual shape of the particular amputation stump. The prosthesis socket of the prosthesis is then pulled over this liner such that the inner face of the prosthesis socket is directed toward the liner and therefore toward the amputation stump. If no separate liner is used, the inner face of the prosthesis socket directly faces the amputation stump. Alternatively, a sleeve, for example, can also be pulled over the amputation stump and provides an airtight seal between the upper edge, i.e. proximal edge, of the prosthesis socket and the amputation stump. In order to fix the prosthesis socket and therefore the prosthesis at the desired place, and to ensure this even when the patient performs considerable movements for example, it is known from the prior art to generate an underpressure between the liner and the prosthesis socket, by means of which underpressure the prosthesis socket is held in its position. Arrangements of very different kinds are known for this purpose.
Generally, the prosthesis socket has a distal through-opening to which a vacuum pump is attached. An arrangement of this kind is known from WO 2006/135851 A2, for example. The vacuum pump, together with a power source provided therefore, is part of the prosthesis set-up. If such a prosthesis is worn over a fairly long period, for example for one day, it is possible for air to penetrate into the volume between the liner and the inner face of the prosthesis socket on account of the movement of the amputation stump and of the prosthesis socket and because of small leaks. The underpressure is thereby reduced, as a result of which the fastening of the prosthesis to the amputation stump is weakened.
For this eventuality, the person wearing a prosthesis described in WO 2006/135851 A2 always has on him the vacuum pump as part of the prosthesis, and therefore, if the underpressure drops, he is able to reactivate the pump and adjust the underpressure to the desired strength.
A disadvantage is that a pump of this kind, which is often designed as a diaphragm pump, is heavy and takes up a lot of space, and it cannot therefore be accommodated in every prosthesis. Moreover, a sufficient power supply has to be provided, for example in the form of batteries. In addition, diaphragm pumps have to be supplemented by valves which, if they become dirty, can impair the reliable function of the pump. To be able to use a diaphragm pump both as a vacuum pump and also as a release pump, elaborate valve circuitry is also necessary.
To overcome this disadvantage, it is known, for example from U.S. Pat. Nos. 5,702,489 and 6,926,742, to provide an external vacuum pump. The disadvantage of this system, however, is that the person wearing the prosthesis always has to carry the pump around as a separate component, so as to be able to attach the pump in the event of a possible pressure loss between the liner and the prosthesis socket. Moreover, he then has to attach the vacuum pump to a corresponding device, which can be provided on the prosthesis socket for example, which proves difficult, if not impossible, particularly for elderly persons or persons of reduced mobility who wear prosthesis systems.
Regardless of whether an external or an internal vacuum pump is provided for a prosthesis, these systems all have a valve system which, once the underpressure has been set, ensure that air cannot penetrate into the volume between the liner and the prosthesis socket. Valves of this kind comprise movable parts and are thus susceptible to becoming dirty and malfunctioning and, accordingly, they require considerable maintenance. In addition, production is relatively complicated and expensive. Another factor is that valves may also be accidentally or incorrectly operated by the person wearing the prosthesis, with the result that air can penetrate into the volume between the liner and the prosthesis socket. In this case, a secure fit of the prosthesis on the amputation stump can no longer be ensured.